One of methods for measuring the surface shape of a measurement object is to use illumination light utilizing laser light or the like, and capture an image of reflected light from the measurement object of the illumination light to measure the surface shape of the measurement object.
For example, Patent Literature 1 below discloses a technology of, using a moving strip-shaped body (e.g., a steel sheet) as a measurement object, measuring a surface shape of the strip-shaped body on the basis of the principle of an optical lever. Specifically, in Patent Literature 1, linear light applied along the width direction of the strip-shaped body is specularly reflected to be projected on a screen, and a reflected image on the screen is captured by an area camera; thus, a stripe image is obtained. After that, the surface shape of the strip-shaped body is measured by performing predetermined image processing on the obtained stripe image.
In addition, as a technology similar to Patent Literature 1, though it is not a technology based on the principle of an optical lever as disclosed in Patent Literature 1, Patent Literature 2 below discloses a technology of applying light beams of laser light to the surface of a planar object to be inspected, projecting, on a screen, reflected light of the light beams off the surface of the planar object to be inspected, and then observing light and dark on the screen caused by sparseness and denseness of the light beams due to unevenness of the surface of the planar object to be inspected.